The d13C anomaly in the northeastern Atlantic

• Published in: Global Biogeochemical Cycles
• Main Authors: Keir, Robin, Rehder, Gregor, Suess, Erwin, Erlenkeuser, Helmut
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU (American Geophysical Union) 1998
• Subjects: Northeast Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/3616/; https://oceanrep.geomar.de/id/eprint/3616/1/Keir_et_al-1998-Global_Biogeochemical_Cycles.pdf; https://doi.org/10.1029/98GB02054

The δ13C of dissolved inorganic carbon was measured on samples collected at 49°N in the northeast Atlantic in January 1994. Deeper than 2000 m, δ13C exhibits the same negative correlation versus dissolved phosphate that is observed elsewhere in the deep Atlantic. Upward from 2000 m to about 600 m, δ13C shifts to values more negative than expected from the correlation with nutrients at depth, which is likely due to penetration of anthropogenic CO2. From these data, the profile of the anthropogenic δ13C decrease is calculated by using either dissolved phosphate or apparent oxygen utilization as a proxy for the preanthropogenic δ13C distribution. The shape of the anthropogenic anomaly profile derived from phosphate is similar to that of the increase in dissolved inorganic carbon derived by others in the same area. The reconstruction from oxygen utilization results in a lower estimate of the anthropogenic δ13C decrease in the upper water column, and the vertical anomaly profile is less similar to that of the dissolved inorganic carbon increase. A 13C budget for the atmosphere, ocean, and terrestrial biosphere indicates that within the range of probable ocean CO2 uptake the ratio of δ13C to inorganic carbon change should be mostly influenced by the 13C inventory change of the biosphere. However, the uncertainty in the ratio we derive prevents a strong contraint on the size of the exchangeable biosphere.